Since the late 1960's there has been increasing concern about the manner in which municipal solid wastes are collected and disposed of and because of increased environmental concerns recycling now has global attention. Problems and costs associated with the disposal of the solid waste have begun to alarm the consumers, producers and politicians. Some attempts to reduce the wastes by recycling have been initiated recently. However, no completely satisfactory way to recycle all types of waste paper have been found as yet.
Paper and paperboard waste is found to be the largest among the municipal solid wastes. In the U.S. it ranged from 24.5 million tons disposed in 1960 to 49.4 million tons disposed in 1984, and is projected to be 65.1 million tons in the year 2000. The paper share of the municipal waste stream has ranged from 30% in 1960 to 37.1% in 1984, and is projected to be 41% in the year 2000. Most of the municipal solid waste is currently disposed of in landfills. However, available landfill space is rapidly decreasing and landfill costs are increasing. Uses for the municipal solid wastes, especially paper and paperboard must be found. Ideally, they should be converted from a negative value residue into a revenue generating product or even value-added products. Since paper and paperboard waste has the largest share of municipal solid waste, attempts must be taken to reduce it.
Pressure is being applied on the pulp industry by regulatory authorities to recycle newspaper. This however involves substantial costs, making the industry hesitant because it may be more expensive to recycle than producing pulp from wood chips. Some of the costs for recycling involve collection, transport and providing facilities capable of performing the recycling tasks including de-inking. De-inking has to be done with solvents resulting in another stream of pollutant which is environmentally unfriendly. For this and many other reasons the industry is reluctant to recycle used newspaper. As far as fine paper is concerned, there is little, if any, recycling done at the present time because of the additives in fine paper.
Paper is mainly made from pulp produced from wood chips in which the lignin and hemicelluloses have been removed. With the lignin and hemicelluloses removed, there is no self-bonding properties remaining for use in the formation of fiberboard. Moreover, due to the absence of the lignin and hemicellulose and also the absence of fiber structure and reduced fiber length, products made therefrom heretofore have lacked resistance to water and moisture and also lack wet strength properties. Because of this, paper and the like products have not been considered a suitable raw material for fiberboard manufacture.
Some proposals have been made to recycle newspaper into building products as discussed for example in the teachings of U.S. Pat. No. 3,736,221 issued May 29, 1973 to K. W. Evers, et al and U.S. Pat. No. 4,111,730 issued Sep. 5, 1978 to J. J. Balatinecz.
Evers, et al discloses subjecting dry waste paper of all sorts such as newspaper, magazines, pamphlets, books, shipping cartons, fiberboard and the like to the action of a hammermill thereby comminuting it to "virtually individual fibers", mixing the resultant with a binder such as polyvinylchloride, urea-formaldehyde resin or phenolic resins and subjecting the same to a pressure of about 6000 psi and then baking the compressed mixture at about 250 degrees fahrenheit for six to eight hours. The resultant product is indicated as having a density of about 40 pounds per cubic foot, can be sawed into different shapes, will receive nails and screws and does not easily chip or crack and is thus considered suitable for construction. However, this known technique is a slow and time consuming process and involves costly equipment. By way of example, a press for a 4'.times.8' panel would have to have a capacity of approximately 28 000 tons in order to exert a panel forming pressure of 6000 psi as called for in the prior art teaching.
Balatinecz discloses breaking waste paper up into fragments, examples of which are indicated as being strips one quarter to one half inch wide and in lengths of three to fourteen inches. A binder such as phenolformaldehyde is used to adhere the flakes together and the panel is formed by subjecting the resin coated paper flakes to a pressure of 150 to 1000 psi at a temperature in the range of about 200 to 450 degrees fahrenheit. The paper flakes are said to be conditioned to a moisture content from 6% to 12% by weight of total dry paper before being blended with the resin binder.
These known and patented procedures do not, however, provide panels that are resistant to moisture and thus do not display good dimensional stability. This is yet another reason why panels formed from recycled paper have not hitherto met with commercial success.
There are different proposals for making manufactured composite board resistant to moisture giving the panel dimensional stability. One such proposal is found in the teachings of U.S. Pat. No. 3,919,017 issued Nov. 11, 1975 to P. D. Shoemaker et al. The process involves bonding cellulosic materials under conditions of elevated pressure and temperature using a particular binder system. The patentee speculates cross-linking occurs between the cellulosic material and the binder system under the conditions of elevated pressure and temperature. The patentee teaches using particles of wood or other cellulosic material defined as including "any material substantially formed from cellulose including natural material such as comminuted wood, vegetable fibers such as straw, corn stalks and other cellulosic materials such as pulp, shreaded paper and the like".
What takes place chemically, when treating wood, is a complex and complicated field and while one can speculate theoretically what might happen it is impossible to say precisely what might be occurring. Other proposals in the formation of composite wood products involves subjecting resin coated wood particles to steam and pressure and heat which may be done on a moving bed for the product as taught by U.S. Pat. No. 4,605,467 issued Aug. 12, 1986 to F. Bottger, or in a single mold (effectively a batch system), as taught in U.S. Pat. No. 4,162,877 issued Jul. 31, 1979 to D. W. Nyberg.
Other patents of interest are as follows.